1. Field of the Invention
The invention is related to loose parts monitor systems on commercial nuclear power plants and in particular to an impact hammer used to calibrate the time delay and amplitude response characteristics of a loose parts monitor system.
2. General Background
A loose parts monitor system (LPMS) is installed on most commercial nuclear reactors in response to U.S. Nuclear Regulatory Commission Regulatory Guide 1.333. As stated therein and well known in the industry, the presence of a loose part in the primary coolant system may be indicative of degraded reactor safety. A LPMS is required to be capable of detecting a metallic loose part that weighs from 0.25 lbs. (0.11 Kg) to 30 lbs. (13,6 Kg) and impacts with a kinetic energy of 0.5 ft.lb. (0.68 joules) or more on the inside surface of the reactor coolant pressure boundary within three feet (0.91 meter) of a sensor. It is further required that the alert logic of the system have the capability to distinguish the transient signal caused by the impact of a loose part from the normal background signals associated with hydraulic, mechanical, and electrical noise and large-amplitude electrical transients.
As known in the present state of the art, the conventional method for calibrating the LPMS is to impact the outside of the primary pressure boundary with either free falling weights or pendulum weights. The impact energy is determined from the product of the mass of the weight times the height from which it is dropped. This data is then used to calibrate the LPMS time delay and amplitude response characteristics. However, this method of using free falling or pendulum weights can be difficult to control and is often impossible to implement for surfaces where impacting must be in an upward direction.